Many types of cable actuated switches are known to those skilled in the art. Cable actuated switches are typically used in applications where an emergency stop capability is required along an extended distance, such as assembly lines. Manufacturers, for example, typically use cable pull safety devices as a low-cost emergency stop device for long conveyor lines or large machines. In certain conveyor system applications it is often necessary to provide a means for operators to actuate the emergency stop condition from many different locations along the conveyor.
Cable activated switches that have been provided generally include a switch support body that has a bore there through. A first switch contact member is generally retained on the body and a second switch contact member is further slidingly retained on the body and insulated therefrom. Clamping means are typically provided for securing the cable passing through the bore. First resilient mechanisms are also provided to bias electrical or manual contact members. During operation, or reaction to a safety hazard, first and second contact members are displaced relative to each other by predetermined axial movement of the cable that passes through the support body. The result is generally the emergency termination of industrial or manufacturing mechanical processes.
Cable controlled electrical safety switch devices have also been provided that include a piston tensioning cable under the action of a spring via a rod and a screw thread for adjusting the tension of the spring and of the cable. A piston groove actuates a push member for the switch. The piston can be angularly adjustable. When the cable is long, a high tension is selected so the groove flank moves away from the push member. Distancing is desirable in such systems in order that any length variations due to heat, which are greater with a long cable, may be prevented from triggering the switch. The clearance between the other flank and the push member is then corrected by rotation of the piston.
Because electrical switches for preventing an accident in a mechanism employing a control cable can generally be included in a casing having a pair of contacts at opposite inner side surfaces thereof and an insulator member having a movable contact, an insulation member may be configured such that it is slideably and axially moved within the casing in connection with tensile force of inner cables. When the inner cables become inoperable because of some problem, the movable contact is touched to the contacts provided on the inner side surfaces of the casing in order to detect the problem or to stop the movement of the mechanism.
U.S. Pat. No. 5,665,947, which issued to Falcon on Sep. 9, 1997, and is owned by the assignee of the present invention, describes a cable switch actuating mechanism, which is provided with a shaft, and a cam structure that slides on the shaft. When the associated cable is pulled to exert an axial force on the shaft, the cam actuator is pushed by the shaft into a deactuating position that moves a switch operator plunger against a plunger of an associated electrical switch. If the cable breaks, the reduction of force on the shaft allows an internal spring to move the shaft against the cam structure and, as a result, move the switch operator into its deactuating position. Appropriate gaps between the opposite ends of the cam structure and associated surfaces of the shaft were provided by design to allow for thermal expansion and contraction of the cable without adverse affects on the mechanism.
U.S. Pat. No. 5,821,488, which issued Oct. 13, 1998, is an improvement over the cable operated switching mechanism described in the '947 patent described above and is also assigned to the assignee of record for the present invention. The improvement is the provision of a latch device associated with a reset plunger which is movable between a normal operating position and a resetting position, wherein the cam structure is moved by the reset plunger to unlock the switch operator when the reset plunger is moved to the resetting position. The positive locking method of the cable operated switching mechanism latches a cam structure in place after the cable is pulled by an operator and does not permit the cam structure to return to its normal operating position until manual intervention is used to push a reset plunger. The cable operated switching mechanism provided a positive stop by incorporating a tab on a latching device, which is associated with the reset plunger and moves with it when a reset button is pushed.
The tab of the latching device slides along a first surface of the cam structure until the cable is pulled to activate the mechanism. Then, under the influence of a spring, the latching device moves upward to cause the tab to move into a blocking position relative to a second surface of the cam structure. The tab prevents the cam structure from moving from its actuated position to its normal operating position until a reset button is pushed. This mechanism overcomes a possible problem wherein a loosely assembled cable, with too much slack, could otherwise allow a switch to be activated by the mechanism, following deactivation by an operator pulling the cable.
U.S. Pat. No. 6,501,040, which issued on Dec. 31, 2003 and is owned by the assignee of the present invention describes a dual directional cable actuated emergency stop device is provided having two shaft assemblies attachable to respective cables spanning along an industrial and/or manufacturing operation. The first shaft assembly is slideably disposed within a housing structure and movable relative to the housing structure along a first path in a direction parallel to an axial centerline of the shaft in response to a force exerted by a cable attached to an end of the first shaft. The second shaft assembly is slideably disposed within the housing structure and movable relative to the housing structure along a second path in a direction parallel to an axial centerline of the shaft, and opposite movement of the first shaft, in response to a force exerted by a cable attached to an end of the first shaft.
A switch operator movable along a second path between a first position and a second position is responsive to movement of the first or second shaft assemblies and is also responsive to a mechanism for locking the switch operator in a second position after the switch operator moves into a second position. At least one electrical switch associated with the device can be actuated when the switch operator is in the second position and deactuated when the switch operator is in the first position. Windows formed on the device housing cover allow a user to monitor tension of first or second cables attached to respective first and second shaft assemblies, based on the position of a cam associated with each shaft assembly.
When long cable lengths are used in association with a cable actuated switch, changes in temperature can activate or deactivate the switch because of the resultant changes in the length of the cable as a result of the cable's thermal coefficient of expansion. With regard to the expansion or contraction of the cable as a result of temperature change, it is much more common for most cables to experience high temperatures during extended use than when the cable was initially installed. In some environments, opposite extreme conditions may exists (e.g., lower temperatures than experienced during initial installation). This occurs because many applications of cable-actuated switches are used in circumstances, such as warehouses, where there may be large variation in temperature that affect the cables characteristics. Furthermore, heating or air conditioning may or may not be provided for winter or summer conditions in such environments. As a result, heating systems are able to maintain the apparatus at normal operating temperatures during winter months, but no air conditioning systems are provided to maintain the apparatus at normal operating temperatures during summer months. As a result, the cables can expand beyond their normal lengths during summer months.
Rather than provide numerous emergency stop switches at multiple locations along the equipment, it is sometimes deemed economically advantageous to provide a single switch that can be actuated by pulling a cable that may extend along, for example, a conveyor system from the switch to a remote location. Although the majority of cable pull devices are single direction units capable of spans up to around 200 feet, some dual directional units do exist, which in effect double the span to around 400 feet. With such long spans of cabling, malfunctions and/or false activations can be prevalent. For example, teasing of the device is found where electrical trip happens prior to mechanical trip.
In a teased condition, the normally closed contacts would be open, but the normally open contacts would remain open. The normally closed contacts typically shut down the machine, and the normally open contacts typically signal (e.g., light, etc.) that the device was tripped. Therefore, if the device is teased, the machine could shut down without any indication of the source. On long conveyor lines or large machines, this situation is costly and frustrating.
Another problem with such prior art devices is the difficulty associated with their set up. For example, to reset (e.g., place in run mode) a cable pull device, the cable must be set to a proper tension. Determining proper cable tension for accurate operation can be difficult. It may also be difficult to determine if the system or device is in the proper run or off state.
It would be advantageous to remedy the foregoing and other deficiencies in the prior art and to facilitate the safe employment of manufacturing equipment, or the like. There is a continued need for improvement in safety mechanisms used, for example, with high-speed industrial equipment that is subject to forces that can cause an interruption in the proper operation of the equipment and can result in damage to persons and/or the equipment if the operation is not terminated in a safe manner. Accordingly, embodiments are described and presented as a novel means to address the shortcomings of the prior art.